Ambient Air Temperature Sensor Circuit High Input
The P0073 code indicates that the Powertrain Control Module (PCM) has detected a voltage signal from the ambient air temperature (AAT) sensor that is higher than the expected range, typically above 4.9 volts. This sensor measures outside air temperature and is used for HVAC control and other engine management functions. A high input often points to an open circuit, a short to voltage, a faulty sensor, or a wiring issue.
1. Most Common Causes
- Faulty ambient air temperature (AAT) sensor with internal short circuit
- Sensor circuit wiring shorted to battery positive (B+) or reference voltage (VREF)
- Open circuit in the sensor signal return wire or ground line
- Corroded, oxidized, bent, or disconnected sensor connector
- Intermittent or permanent failure in the control module (PCM/ECM/BCM)
2. Symptoms You Will Notice
- Inaccurate outside temperature display
- HVAC system malfunction (e.g., incorrect auto temperature control)
- Check Engine Light illuminated
- Possible impact on engine performance in some vehicles
3. Step-by-Step Diagnosis
Step 1: Use an OBD2 scanner to confirm the code and check for other related codes.
Step 2: Visually inspect the AAT sensor and its connector for damage, corrosion, or loose connections.
Step 3: Measure the voltage at the sensor signal wire with the ignition on; should be around 0.5-4.5V depending on temperature. If voltage is near 5V, suspect an open or short to voltage.
Step 4: Disconnect the sensor and check resistance; compare to manufacturer specifications (typically 2-10 kΩ at room temperature).
Step 5: Check for continuity and shorts in the wiring between the sensor and PCM.
4. Frequently Asked Questions
Is it safe to drive with this code?▼
Yes, it is generally safe to drive, but the HVAC system may not function correctly, and the Check Engine Light will be on. It's best to diagnose and repair soon to avoid potential drivability issues.
How much does it cost to fix?▼
The cost typically ranges from $50 to $150, including parts (sensor $20-$50) and labor (0.5-1 hour).
5. Commonly Affected Makes
This is a generic OBD2 code, potentially applicable to any manufacturer using this diagnostic standard.